Dark Water
by tj1919
Summary: Dipper and Mabel get more than they bargained for when they go searching for Wendy's secret swimming hole. This story is set after the season 2 episode Scary-oke and does contain minor spoilers.


Via AFF user Lenox

"Dipper, can't you put that book away for just two seconds?"

"No Mabel, I can't. When Stan took the journal away from me, I thought I didn't need it. But now that I've got it back, I want to study it as much as possible, just in case I lose it again."

"But Dipper, we've been through this," Mabel groaned as she sat on the floor beside her brother. "You stopped Gideon and his giant robot without the journal."

"I know, sis. But it doesn't have anything in here about giant robots… I think. Look Mabel, I get what you're saying. But there's so much we don't know about what's going on in this town."

"Dipper, I'll admit there's been a lot of weird stuff happening, but I'm not about to let it get in the way of my summer. And besides, we'll still have some interesting stories for when we get home. So what are you working on, exactly?" Dipper lay on the floor of the Mystery Shack's gift shop. After their re-opening celebrations, and de-zombifing Soos, it had gone back to the slow, dull days of their great Uncle Stan just waiting for the next bus load of tourists... or suckers, as he called them. And while Dipper and Mabel were covering for Wendy during her lunch break, Dipper had taken over the floor with his journal, a pen, and a pad of paper. Mabel grabbed the pad from under him and looked over the multiple rows of letters that her twin brother had scribbled over the page.

"It's a cipher, Mabel. This journal brings up all these different jumbles of letters. And my cipher here helps me work out what it means."

"Like a secret code!" Mabel cried, throwing her arms up into the air.

"Exactly. You see this one here?" He asked, pointing at the page. "You have to swap the letters around. You swap A for Z, B for Y, and so on." Mabel replaced the pad of paper and picked up the journal. She flicked through the blank pages until she found her brother's entries. She realised that she hadn't actually read through the stuff he wrote.

"Some of these sketches are pretty good, bro-bro. But I noticed you went to put your real name here," Mabel held the book open under her brother's nose, pointing at his introductory page.

Name: M Dipper Pines

"I know, I know," Dipper rolled his eyes. "It was a momentary lapse in judgment." Mabel, deciding not to press the issue, continued to flick through the pages. She saw the entries on Old Man McGucket, Wendy, and Dipper clones #3 and #4, plus her own entries on the Land of Smile Dip, Waddles, and Mermando.

"So, what does your code say?" Mabel asked as she placed the book back on the floor. Dipper returned to his notes as he quickly worked it out. But before he could answer her, the Mystery Shack door swung open and Wendy stepped inside.

"Hey guys, did I miss anything?" Wendy asked as she took her spot back behind the counter.

"Nah, Grunkle Stan and Soos are off somewhere coming up with who-knows-what to sell to people," Mabel just rolled her eyes at the lengths Stan would go to con money from his customers.

"Hey Wendy?" Dipper asked as he pointed his pen at her. "Why is your hair wet?"

"Oh, it didn't dry? Damn. I spent my lunch break swimming. I found this sweet little swimming hole in the middle of the woods a while back. Sometimes I head out there and just chill for a while."

"Re… really?" Dipper nervously asked. He could feel his cheeks turning redder with each passing second. "A secluded pond… out in the woods?" he gulped, his mind filling with thoughts of him and Wendy alone in such a place.

"Yeah dude, but it's for skinny dipping only," Wendy said with a wink.

"Skinny… dipping?" Dipper gulped. He was praying that his blushing cheeks weren't that noticeable. Wendy didn't seem to pick up on his nervous behaviour, but Mabel was doing her best to stifle her laughter.

"Look, I better dry off properly before Stan gets back. Be back in a few." Wendy strolled passed the twins and pushed through the 'Employees Only' door on the far side of the shop. As soon as she was out of sight, Dipper gathered his things and stood up.

"And what just where do you think you're going?" Mabel asked as Dipper walked towards the door. He turned and gave Mabel the most determined look on his face. Aside from finding the author, Dipper had never been more certain about anything in his life before this moment.

"To pack a bag. I'm going to find that pool."

"Whooo! Adventure! Whooo-whoo," Mabel cried as she climbed over a log. With the journal tucked safely at the bottom of his backpack, Dipper looked over a large map of the forest. He'd been able to work out the places he and Mabel had already explored based on various landmarks, but the Pines twins were now in unknown territory.

"Mabel, do you have to yell that every time you cross a log?"

"Sorry bro, but I just can't help myself sometimes. I sense adventure. Adventure!" Mabel cried again, pulling her arms back into her sweater sleeves and flapping them about as they walked. "And besides, I know the real reason you're out here."

"Reason?" Dipper asked, his nerves returning to his slowly cracking voice. "I just... you know, feel like a swim."

"If you wanted to swim, we could have gone to the town pool. We knew where that is and we're not going to get lost. And besides, you've already gotten lucky once because of that place," Mabel joked, nudging her brother with her elbow.

"Mabel, for the last time, I did not kiss Mermando. It was mouth-to-mouth resuscitation and you know it."

"Kisses are mouth-to-mouth Dipper," she teased. "But I think you wanna find this pool so you can spy on Wendy. And now that I think about it, that's pretty low."

"What? No. No! I just… it's such a warm day and I figured that a quick dip would be nice." Dipper awkwardly began to rub his elbow, and his eyes darted from side to side as he made up his excuse on the spot.

"Yeah, you wanna watch Wendy.

"Okay fine, I admit it, and I want to be able to come out here with her too. Just don't tell anyone."

"Oh Dipper," Mabel said as she pat him on the shoulder, "your secrets are safe with me."

The twins made their way deeper into the forest, looking or listening for any signs of water. It suddenly occurred to Dipper that not only did he not have any idea where this pool was, but he had also no idea of what it looked like. It could have been one of many different small lakes and ponds in the woods. When he imagined it while Wendy was talking, he pictured a small lake in the middle of the forest, filled with sparkling clear water, thick and tall trees circling the sandy bank, and the sun shining down in patchy holes through the canopy. He pictured a hidden paradise, one would make the perfect setting for a romantic afternoon. But the further they went from the Mystery Shack, Dipper's hopes of finding the hidden pool began to dwindle.

"Dipper, we've been searching for hours. How about we just go back?" Mabel groaned as she stood by another log, before promptly collapsing against it. Dipper knew she was exaggerating, they'd been out for a little over an hour and they both knew it. His map showed no mention of any pool or lake, or even a river or waterfall. But according to the map, they had already circled back towards the Mystery Shack. At least the return walk wouldn't be as long. Dipper didn't want to admit defeat, but he was getting a little tired. He decided that he could always ask Wendy where it was.

"Yeah, I guess you're right. Come on Mabel, let's go home." Mabel got to her feet and started to make her way back. Annoyed, Dipper picked up a small rock and threw it into the trees. He turned to follow his sister home but froze when he heard a faint splash in the woods. The twins looked at each other in disbelief. Mabel picked up a rock and tossed it at Dipper, who caught it and threw it again. After a couple seconds, they heard another soft splash. With excited smiles, the twins ran towards the log that Mabel fell against. They climbed over it and ran through the trees. And just as Dipper had imagined, there it was.

"This is it. This has to be it!" Dipper cried as he slipped his backpack from his shoulders and fell to his knees by the pond. He cupped his hands in the water and splashed it over his face. He instantly felt refreshed and rejuvenated, as if his tiredness and soreness from trekking though the woods had been washed away. He let himself fall back onto the soft, lush grass. With the dim light of the warm sun shining down through the canopy, he felt like he was lying on a cloud. The ground was that soft and that comfortable, he felt as if he could just doze off.

"Whoooooo-whooooo. Coming through!" Mabel cried out from beside him. She had stripped down to her pink bathing suit and was running towards the water.

"No Mabel, we don't know how deep… " but Mabel didn't listen. She launched herself into the air and jumped into the water, causing a huge splash as her body broke the surface. She rose a few seconds later, beckoning her brother to join her.

"Hey Dipper, come on in. The water's perfect."

"Sure thing sis. Just give me a sec to… to… Mabel, where's your suit?"

Both Dipper and Mabel looked below the surface of the water, and the bright pink swimsuit was nowhere to be seen.

"What? Hey, where'd it go?" she asked loudly, before starting to swim in circles. Dipper brought his hand up to the side of his face. His sister may be out in the water, but he could only make out the lack of her bright pink suit.

"Uh…Mabel, shouldn't you… I don't know, cover yourself up or something?"

"Pffft, nah. Come on Dipper, we used to take baths together. Besides, this water's so great that I don't really care.

"You don't care?" Dipper asked before staring intently at the water. "Mabel, it was a one-piece swimsuit. There's no way it could have come off when you jumped," he cried out to her as he took a few steps further.

"Dipper, come on. I told you, the water's fine. I'll swim over here if it makes you more comfortable. You said you wanted a swim, so come on. You can't just stand in the shallows like that."

"The shallows?" Dipper asked before he looked down at the ground. He hadn't realised it, but those few steps he took had carried him into the pond. He suddenly realised that Mabel was right. The water was perfect. Not just good, not just great, but perfect. Dipper suddenly felt better… about everything. He wasn't sore or tired from his hike, he wasn't worried or curious about mysteries of the town, and he didn't seem to care anymore that his sister's bathing suit had seemingly vanished. But as he stood up to his ankles in the water, he realised something was wrong.

"Where'd my shoes go?" he looked down into the water.

"What'd you say Dipper?" Mabel asked from the far side of the pond. Dipper looked down into the water. He didn't remember taking his shoes or socks off, and yet he could only see his bare feet below the surface. He could feel the sandy lakebed underneath his toes. Dipper looked around the bank for any sign of his shoes, he couldn't see them by his bag, yet he was certain that he never took them off. But when Dipper stepped back up onto the bank and lifted his leg out of the water, his shoe reappeared on his foot. It was bone dry, as if it had never been submerged. But as Dipper lowered his leg back into the water, the shoe vanished again and he could feel the wet dirt under his foot.

"Huh, now I get it," he said as Wendy's words rang through his head. "The pool is for skinny dipping _only_. Clothes vanish when submerged. This would be a great place to film one of my Guides to the Unexplained. No wait, MABEL, DON'T!" Dipper was too busy focusing on his latest discovery that he didn't notice his sister swimming up to him. Before he could do anything but protest, she grabbed his arm and pulled him into the water.

Mabel didn't seem to care about Dipper's discovery of the water. She didn't care that her swimsuit didn't seem to exist below the surface. And she didn't care that her brother's clothes were vanishing as she pulled him in.

"Mabel, stop. Let me go!" Dipper cried in protest, but his cries fell on deaf ears as his sister pulled him towards the middle of the pond. The ground fell out beneath their feet and Dipper found himself treading in the open water. Finally, Mabel loosened her grip as she started to splash around and Dipper was able to pull free from her grasp. He made a mad dash for the shore, swimming as fast as his arms would allow. But as he got closer, he began to lose the urge to get out. Dipper stopped and just let himself float there. He looked down and could see his naked body below the clear surface of the water. Behind him, Mabel continued to splash and swim. The desire to get out had simply vanished. And now, suddenly, all he wanted to do was swim. The water clearly had some sort of magical properties. First it made their clothes disappear when submerged below the surface, now it was starting to affect Dipper's state of mind. He didn't know why he didn't get out. All he knew is that, all of a sudden, he didn't want to leave. He looked behind him. Mabel was still oblivious to their situation, but she seem to didn't care. The pool felt incredibly refreshing on the hot summer's day, another side effect of the water. Falling to its power, Dipper swam back to his sister.

The twins lost rack of time as they splashed and played. They held a swimming race from one side to the other. Mabel would frequently slip below the water to grab Dipper's legs and pull him under. They decided to see who could hold their breath longer, and Dipper's hat would reappear on his head as he surfaced. They didn't care how long they had spent in the pond. Had it been an hour? Maybe two? All they knew is that they didn't feel like worrying about anything. It was like all their cares had been washed away, leaving them both in a state of pure relaxation.

"So do you think we should head back soon?" Dipper asked as Mabel floated by on her back.

"I'm in no rush," his sister said. "It's nice out here. And besides, I got nothing else to do today," Dipper raised an eyebrow.

"You mean you actually did something around the Shack?" he asked in a slightly condescending, yet joking, tone of voice.

"Of course. I picked out which letters I'd pass on to Grunkle Stan," Mabel said as she let the lower half of her body sink back into the water. Dipper slapped the palm of his hand against his face.

"Mabel, we've been through this. You can't just go through Stan's mail, forward five letters to him and read the rest. What if it's something important? Or private?" The twins looked at each other for several seconds in silence, before letting themselves succumb to laughter at Dipper's joke. While Grunkle Stan did get regular mail, it was almost never anything important. It was a good solid minute before Dipper found himself able to talk again, and he wiped a tear from his face.

"But seriously though," he chuckled, "you should really stop."

"Oh come on Dipper. You've got your journal, I want to have a little fun poking around too. I mean, this vacation's been a blast, what with Gideon, the fight with Bill, and... and Waddles! Now we've got this pond as well."

"Yeah, although too bad I can't enjoy it properly with my naked sister hanging around," Dipper chuckled. He meant it purely as a joke, but his laugh quickly vanished once he saw the stern look on Mabel's face. She turned around in a huff and swam towards the edge of the pond, leaving Dipper treading in the water.

"What? Mabel, come on. I was just joking," Dipper called out before he started to swim after her. Mabel didn't say a word until she reached the grassy shore, her bathing suit re-appearing on her body as she stepped out of the water.

"Mabel, I'm sorry okay. I didn't mean it," Dipper realised that he'd crossed the line, even in jest. He and Mabel had always gotten along growing up together, but he'd upset her before. The image of her banging her head against a totem poll for a full month came back to him, the end result of their last argument.

"Tell me," Mabel said as she slipped the shoulder straps from her swimsuit down her arms. Once her hands were free of the loops, she pulled the rest of the suit down her body and stepped out of it, leaving it discarded on the ground. She stood proud, yet mad, on the edge of the water.

"What's so unappealing about so unappealing about MY body?" she demanded. Dipper hesitated, finding himself unable to move or answer. He and Mabel had spent the last hour at least swimming naked. But it wasn't until now that Dipper was able to get a decent, proper look at his sister. Standing in the light, out of the water and in plain view, Dipper could see two very slight bumps on her chest as her budding breasts were starting to form. His eyes travelled downwards, taking in the sights of her stomach, smooth legs and the bald slit between them.

"And what about from this side?" Mabel asked as she spun around. Her long and wet hair swayed against her back as she moved. With her fists on her hips and turning her head to look at her brother behind her, she made sure Dipper had decent, proper view of her ass.

"Awww, geez. Come on Mabel," It was only now that Dipper lifted his hand to cover his eyes. But Mabel could already see the effect that she was having on his body. Dipper was in the shallows of the pond, with his waist below the water line. Standing bottomless on the slanted bed of the pond, Mabel could clearly see her brother's erection forming below the water. With a smug look on her face, she face him and crossed her arms. Maybe it was an effect from swimming in the strange water, but Mabel could resist taking an eyeful of Dipper's arousal. But at the same time, she didn't want to appear to stoop to the simple ogling that he did to her.

"Well?" she asked, with a smirk on her face.

"Mabel, come on. Is this really necessary?" Dipper asked. He never meant for such a simple joke to sound so offensive. "Look, I'm sorry okay? I didn't mean it." As Dipper apologized to his sister, neither he or Mabel spotted the rustling grass on the far side of the pond. They didn't see the figure, cloaked in the shadows of the trees, slowly make its way around the water's edge.

"Oh, Dipper," Mabel finally said as she sat down on the grass and hugged her legs against her chest, "I know you didn't mean it. But I do wish you'd be a little more sensitive in future."

"Mabel, I think we should leave. This pool is great and all," he said as he cupped some water in his hand and lifted it above the surface. He watched the clear liquid seep through his fingers and fall back to the pond. "But this pond has done something to us. It's making our clothes vanish below the surface..."

"Yeah, I can see that Dipper." Mabel smirked.

"... and it's making us act weird too. Like, I know you can see me and I can see you, and I know that we shouldn't be like this around each other. But it just feels right, like I'm comfortable with it when I know I shouldn't be. It's almost as if..."

"As if you don't care?" A voice rung out from the trees behind Mabel, and the shadowy figure emerged from the forest.

"Wendy?" Dipper asked as the fifteen year old stepped out onto the grassy bank. Mabel, who quickly realised that she was naked, squealed as she ducked behind a tree. Now she was out of the pond, the effect of the water was wearing off.

"I figured you two would be out here." she chuckled. And, very calmly, picked up Mabel's swimsuit and tossed it on the ground beside her. Crouching down with a hand covering her crotch, she reached out to pick it up.

"Shouldn't you be back at the Shack?" Dipper asked as he walked out of the pond, his clothes reappearing on his body as he surfaced. Wendy just shrugged her shoulders.

"Dude, my shift ended half an hour ago. You guys have been out here for a couple of hours."

"H... hours?" Dipper stammered.

"Well, we were searching the woods for a while," Mabel said as she emerged from behind the tree, her pink swimsuit back on her body. "It must be getting pretty late in the afternoon."

"So... why are you back out here?" Dipper asked, hoping that Wendy wouldn't pick up on the nervousness in his voice.

"Are you kidding Dipper? Do you even know what this place is? What it does?"

"How it makes your clothes vanish and gets you acting all weird?"

"What? No. Well, partially. Geez, it really doesn't work for you?"

"What doesn't work?" Dipper asked, his interest suddenly peaking. After already been exposed to the magical water, he was suddenly worried that he and Mabel were in for another unexpected surprise from the mysterious pond.

"There's this rule... this thing it does. I can't explain it, but when two people swim in the pond, the water just draws them to one another. Soon, they can't help themselves."

"Help... themselves?" Dipper was confused. He didn't know what Wendy was talking about.

"Oh boy," Mabel muttered to herself. A smile crossed Wendy's lips as she took Dipper's hand and stepped into the water. Dipper gulped, watching as her boots and pants vanished below the water.

"Maybe it's because you're too young, or you haven't been in here as long as I have. The water makes two people want to have sex Dipper."

"Sex?" Dipper asked. Now he really was confused. Wendy suddenly felt awkward.

"Your dad hasn't given you the talk yet?" she asked. Dipper shook his head while Mabel stepped forward.

"Dad didn't, but Stan did gave the talk to Dipper. Or at least he thought he did."

"You've lost me," Wendy said.

"Long story short, Grunkle Stan gave Dipper the talk. But it was me in his body. That was a very weird and... awkward day."

"Uh-huh," Wendy bit her lip, not really sure on what Mabel was talking about.

"Look, the point is that if the two of you were in the pool together, it's going to happen. Either in or out of the water. And the longer you wait, the worse the attraction is going to get. If you do nothing, you're both going to snap and you're not going to care where you are."

"Wendy, that's just... no. No." Mabel said in protest. "I love Dipper, but he's my brother. Something like that.. . no. It's not going to happen."

"So you two were swimming together?" Wendy grinned. She didn't see anything, but she figured that this would happen as soon as the twins left the shack. "And guess what else is going to happen." She smiled at Dipper and then pointed downwards. Dipper followed her finger and saw what she was pointing at. Still hand in hand, they were both standing in the shallows of the pond. He didn't even realised that he'd stepped into the water.

"So... we're going to...?" he asked.

"Oh yeah," Wendy said before she spun him around. She made him face Mabel, who was picking up her clothes and preparing to walk back to the shack. "But your sister's gonna be first. I guess it's like the order or something. I don't know, but it's how it works." Dipper's eyes went wide at Wendy's request. No way, she couldn't be serious.

"Do... does she have to be?" he stammered. Wendy calmly nodded. She knew how this pool worked, and how they were now fated to sleep together.

"Look, Dipper," Wendy said as she knelt down to him, "I'm not kidding here. You and her, it's going to happen. The more you see her, the longer you spend together, the stronger the attraction's going to get. Right now, it's harmless. You could sleep with her and get it over and done with. But if you wait, you're going to want more than that. You're going to actually want to be with her. And it'll get to the point where it'll happen. The two of you are just gonna snap and do each other. It could be awkward if you and she are walking around town. And once the two of you get it on, then it'll be our turn. But that's not going to happen until after you've done it with your sister." Dipper was taking in every word, all while he watched his sister walking off into the trees.

"I'll see you back at the Shack." she said coldly without looking back at them. Dipper looked back at Wendy. She folded her arms and nodded her head towards Mabel, motioning Dipper to go after her. He rolled his eyes and groaned before chasing after her.

"Mabel, wait up," he called as he climbed over logs and around trees, running as fast as his legs would carry him. Mabel chose to ignore him and just kept walking through the woods.

"Mabel, please. Just... come back to the pool. We can talk about this."

"Dipper, it's just a pond. Nothing is going to happen."

"But what if Wendy's right? I mean, look at what it did to us before. We don't know anything about it. Look, Wendy said that..." Dipper realised he was almost begging.

"Oh Wendy said this, Wendy said that, I heard what you two were talking about. Dipper, she's playing you. It's just a prank. Can't you see that?"

"No," Dipper yelled as he stamped his foot on the ground. "Wendy wouldn't do that." Mabel was suddenly taken back. She knew Dipper had feelings for her, but never did she think that he'd actually defend her or her intentions. "Look, I sacrificed a date with Wendy at the carnival so you could win your pig, so I think you owe me on this."

"Dipper, no. Just... no. I'm grateful for what you did back then but... but..." Mabel's voice drifted off, and all she could do was just stare at her brother.

"Mabel? You okay?" Dipper asked. She didn't seem to hear him. It wasn't until Dipper snapped his fingers in her face that she shook her head and snapped out of it.

"Looks like it's starting..." Wendy said as she stepped out from behind a tree. Mabel just glared at her as she walked passed them with her hands in her pockets.

 **"YOU'RE BEING AWFULLY CALM ABOUT THIS!"** Mabel cried after her. But Dipper couldn't help but notice that Mabel didn't deny it.

By the time they got back to the Mystery Shack, Wendy had noticed, and pointed out, each time that Dipper and Mabel glanced at each other. She could feel the water taking effect on her as well, and she was finding it harder to get Dipper out of her head. She noticed how the two of them would just walk side by side in front of her, occasionally and 'accidentally' bumping into each other. When Dipper tripped over an exposed root, Mabel was quick to help him up and brush the dirt off his legs. They looked at each other with loving smiles before Mabel forced herself away. The trio walked in silence as they walked out of the woods, emerging though the trees at the rear of the Mystery Shack.

"Wow, we wandered around out there for a while, didn't we Mabel?" Dipper asked, but Mabel didn't answer. She stoped, almost as if she was considering ignoring him. But Mabel started walking again towards the Shack, purposefully not looking or answering him. Wendy walked up behind Dipper and rested her hand on his shoulder.

"You're feeling it too, huh?" she asked. Dipper just sighed.

"Yep, just a little." The two of them watched as Mabel opened the door and slipped inside. "I don't understand Wendy. If she doesn't want to do anything, why can't you and I just..."

"Whoa, easy there dude. I'm not quite there yet. Look, who went into the pool first?" Wendy asked, having a feeling that she already knew the answer.

"She did." Dipper sighed.

"Then it's affecting her more than it is you or me. The two of you are going to be drawn together Dipper. I know you're feeling something for her now..."

"Yeah, I am."

"... and she's feeling the same thing towards you. Listen Dipper, she _wants_ you. She won't show it but that's how the pond works. And her feelings towards you are only going to get stronger and stronger. The sooner that the two of you let those feelings out, the happier you'll be."

"But why didn't you tell us this before?" Dipper asked. This whole situation could have been avoided if Wendy had said something when she came back.

"Because I didn't think you would actually find it, let alone go looking."

"So what should I do?" he asked. Wendy just sighed. She was starting to fall for Dipper now, she could feel it. Glancing at him in the forest was one thing, but now she was actually seeing him as more than a friend... much more. She didn't want to send him away, not yet. But for his and Mabel's sake, she had to.

"Follow me," Wendy said as she made her way towards the Shack, "and do exactly what I tell you."

The door to their bedroom attic swung open as Dipper stepped inside. Mabel was laying on her bed, her legs high in the air and holding Waddles up with her feet. Her eyes glanced towards the door as it opened, and Dipper could see that her gaze was lingering on him a little too long. Finally, she looked back up at her pet pig.

"Go away Dipper." she firmly said. Dipper ignored her. He had Wendy's instructions fresh in his mind. He didn't leave the room, but he found that he couldn't move forward either. He felt the sharp jab of Wendy poking him in the back and urging him to keep going. If Dipper had so much trouble confronting Wendy about his feelings, then how the hell was he supposed to go through with this? Behind him in the hall, Wendy sighed and rolled her eyes. She was growing impatient. Wendy pushed Dipper into the bedroom and watched him stumble to the floor.

"Whoa! Hey, what gives?" Dipper yelled as he rolled over to face the door. But Wendy had pulled the door shut by the time he sat up, and Dipper heard the familiar sound of the lock clicking into place. With no other option, Dipper got to his feet.

"Look, Mabel..." he began.

"Dipper, shut up."

"Listen to me, if we don't do this then..."

"No Dipper, you listen!" Mabel cried. She dropped her legs and swung them over the edge of the bed, leaving Waddles to fall on the mattress. "I don't know what the deal with that pool was, but there is no way that _that_ is going to happen!"

"But Wendy said..."

 **"I DON'T CARE WHAT WENDY SAID!** What does she know?" Mabel screamed. Dipper glanced over at the locked door for just a split second, unsure if Wendy could hear them. But he had a plan to follow. Without saying a word, he placed his hands firmly on Mabel's shoulders.

 **"LET GO OF ME DIPPER!"** She yelled as she tried to brush him off. But Dipper kept a firm grasp.. He knew that the attraction he was feeling wasn't natural, but nevertheless they were both going through the same thing. Dipper didn't allow his nerves to get in the way.

"Mabel," he said, "I'm sorry. But this is for our own good." He pulled her close, moved one hand to the back of her head. Mabel knew exactly where this was going.

 **"DON'T YOU DARE.** **I'm warning you M..."** Dipper cut her off mid sentence as he placed his mouth on hers and pressed their lips together.

The first moment their lips touched, Mabel was taken completely by surprise. In the next second, she tried to pull free from Dipper's grasp. But the longer their kiss lingered, the less of a struggle Mabel gave. It wasn't long before the twins had their arms wrapped around each other, their lips apart only to make room for their tongues to explore each other's mouths. Waddles watched from the foot of Mabel's bed as the two of them stumbled back onto her mattress. Their kiss broke only long enough for Dipper to pull the sweater off his sister's body, and it resumed as Mabel pulled the vest from her brother's shoulders. They were so lost in the moment that they didn't hear the bedroom door opening. Waddles was the only one who reacted and ran out into the hall. Wendy poked her head into the room. After hearing raised voices followed by a sudden silence, Wendy's curiosity had gotten the better of her.

Walking into the room unnoticed by the twins, Wendy watched as their kiss was broken. Dipper had tugged at Mabel's swimsuit, pulling the strap off her shoulder. He kissed her flat breast, gently sucking and flicking the small nubbin with his tongue. Wendy could hear Mabel's soft, cute moans as she pushed Dipper's hat from his head and ruffled her fingers through his hair. Meanwhile, Dipper lifted Mabel's skirt up around her waist. He slipped his hand into her swimsuit, and gently rubbed his fingers over her virgin slit.

Whoa," Wendy whispered. She was getting turned on by watching the incestuous display in front of her. She hadn't expected them to move so fast. Mabel was groaning on the bed under his touch, and Dipper looked like he knew exactly what he was doing.

"How does he know what to do?" she asked herself. Dipper was twelve years old, probably only just barely starting puberty. There was no way that he had any idea of what he was actually doing to his sister. And yet, judging on how Mabel was reacting, it was if he had done it countless times before.

"Nnngghhhaahhhhhh," Mabel moaned, lifting her whole back off the bed. Wendy, who couldn't keep her eyes off Dipper, could see the position of his hand inside her swimsuit. It was placed directly over her crotch. She was watching Mabel receive her first finger.

"Lucky girl," Wendy said to herself. As soon as the words were out of her mouth, she suddenly realised that she wasn't whispering them. Both Dipper and Mabel froze, staring at each other. Slowly and simultaneously, they turned their heads to look at Wendy. The older girl nervously chuckled. Feeling awkward, she said the first thing that came into her mind.

"So... can I join in?"

Wendy was still quite unclear on the full effect of the pond water. Maybe that's why Dipper knew how to make his sister squirm. And maybe the water is why she knew exactly how to work her tongue over Dipper's shaft. She knelt on the floor between Dipper's legs. Her head was bobbing up and down his erect penis, and her tongue swirling over the tip as she pulled her lips back. Wendy had never done anything like this in her life, or anything ever with another guy. Yet somehow she just knew exactly what do to.

"Hey! He's my brother, and we were in the pool together first," Mabel cried, kneeling beside him. Now that she wasn't fighting her feelings, she was letting jealousy get in the way.

"Mabel, relax. I'm not stealing him from you. I'm... borrowing." Wendy said. Mabel rolled her eyes and folded her arms as Wendy went back down.

"She... she is pretty good Mabel." Dipper nervously chuckled. "Maybe we should just, you know, let her finish?" Mabel scoffed as she sat next to her brother.

"Boys," she muttered, rolling her eyes.

"Relax Mabel, I was just getting him ready for you," Wendy stood up and sat down on Dipper's bed. "He's all yours." Dipper scooted himself back up against the wall as Mabel swung her leg over his shaft. She straddled her twin brother while he pressed his cock against her needy hole. Mabel could barely contain her excitement as his privates brushed against hers.

"You ready?" Dipper asked. His dick was pressing against her entrance and both hands on her hips. Mabel nodded, and Dipper slowly pulled her down. Mabel could feel herself opening up around him. With her knees bent and on the bed on either side of Dipper, she placed her hands on his shoulders as she sank. His dick was a lot thicker than his finger, and she could almost feel herself tearing inside. She felt more discomfort than pain, until Dipper felt himself unable to go any further.

"You sure you want to do this Mabel?" He asked.

"I'm ready Dipper," she said with a soft smile. Wendy watched quietly from the other bed, as Mabel grabbed her pillow and bit down on it. With one swift tug, Dipper pulled his sister down the rest of his length. His dick pierced her hymen and rested inside her. Mabel's muffled screams filled the room, and Dipper and Wendy were suddenly worried that Grunkle Stan might have heard her. Dipper wiped a tear trickling down Mabel's face, and he took the pillow from her jaw. They spent that moment just looking into each other's eyes. Their whole lives they had been doing and experiencing things together. But never did either of them think that they'd give their virginities to each other.

"How's it feel, sis?" Dipper softly asked.

"A little hot, and tingly," Mabel sniffled.

"Did it really hurt that much?"

"It's.. it's okay. I just need a minute."

It wasn't long before Mabel felt she could continue. And when they were ready, Dipper took it nice and slow. Working with Mabel on her knees, Dipper lifted her up along his shaft. Mabel could feel herself being emptied inch by inch. It was a very weird feeling to be filled like this, but even stranger to be emptied. After even just a few seconds, she couldn't help but feel like her body was actually missing it. Slowly and carefully, she and Dipper worked up a rhythm. Gradually, they went faster. And before long, Mabel had forgotten all about the pain of her first time. All she could feel was the pleasure of her brother thrusting inside her. She moved her hands from his shoulders to the wall behind her, pressing and leaning against the vertical surface as they fucked harder and faster. Together they experienced love beyond what normal siblings shared for each other, a forbidden bond that deep down they knew to be wrong. But after being exposed to the strange properties of the water, neither of them cared.

"Almost... there... Mabel," Dipper grunted. As she watched the twins fuck from across the room, Wendy had a sudden thought. Could Dipper actually cum yet? He was only twelve years old and his voice was just starting to crackle. Her thoughts were interrupted with the moaning twins. Dipper had pulled Mabel down over every inch of his shaft, while Mabel shuddered on top of him. Both twins had reached their climax. Their lips met for a passionate kiss as they rode out their orgasms, groaning with lust into each other's mouths. But when their kiss broke, Mabel rolled off her brother. The two lay panting on the bed, and Wendy saw a single drop of pearly white seed fall from Mabel's used pussy.

"Then I guess that settles it," Wendy said as she stood up and unbuckled her belt. Dipper just lifted his head and looked at her as she walked over. With a smile on her face, she crossed the room.

"My turn," she said.

Dipper lay on Mabel's bed, staring up at the ceiling. On his left, Mabel. On his right, Wendy. From the window he could see the night sky and the stars above. Both girls had his cum dripping from their used pussies. He had fucked Wendy and Mabel a couple of times each. He felt tired, exhausted and sore. His and Mabel's bodies had been through so much in the past hour, and Dipper knew that they were still feeling the effects of the water. With a soft moan, he rose off the bed and walked towards his dresser. He pulled the journal from it's draw and opened it up. He had gone through this journal cover to cover on more than one occasion, yet he didn't remember reading anything about the strange pond. He sighed as he flipped though the pages. There had to be something about it. Finding nothing, he closed the book, leaving it to rest in his lap. He looked down at the golden six fingered handprint on the cover, and the giant number in the center.

"Maybe it's in one of the other journals. But I probably shouldn't write about today," he said as he placed the book back in the draw. He pulled the blanket off his bed and walked over to Mabel and Wendy. He sat in the middle and pulled the blanket over them, before snuggling up to his sleeping sister.

The next morning, everything had changed. Dipper had formed a new and closer bond with Mabel and Wendy. Over the next few days, the three were almost inseparable. They would all make their way to the pool during Wendy's lunch break, and satisfy their mystical urges right there in the water. While both Wendy and Mabel had only swum with Dipper, and neither of them had any real attraction to each other, they soon found themselves sharing the cool waters.

"So, is this going to be a… you know, permanent thing?" Dipper asked one day, while sitting on the bank and dangling his feet in the water.

"What do you mean?" Mabel asked as she swam up to him.

"I mean… us. Is there just an 'us' because we've been swimming, or will there keep being an 'us' if we stopped?" Mabel didn't need time to ponder his question. Maybe it was because they'd been swimming so often together, or maybe it was because she resisted after their first dip. But she had an answer already lined up. Mabel grabbed her brother's ankles and pulled him into the pond with a small splash. Mabel pressed herself against him and wrapped her arms around his waist as he surfaced.

"Dipper, whether we've got the pool or not, there will always be an 'us'." With their bodies against each other in the shallows, they leaned in for a kiss. On the other side, Wendy was just floating on her back, turning her head just in time to see the twins' passionate embrace.

"So Wendy, when's your lunch break?" Dipper asked as she sat by the Gift Shop register.

"I don't know Dipper. I think I might just give the pond a miss today?"

"Why? You're not… you're not enjoying it anymore?"

"Dude, don't get me wrong. I love going swimming with you and Mabel. It's the highlight of my day. But I'm thinking that I might just give it a rest today."

"Aww, okay. Mabel, what about you?" Dipper asked.

"Sorry bro, but I think Wendy's got the right idea."

"You're bailing out on me too?" Dipper asked, disappointedly.

"Come on Dipper," Mabel said as she playfully punched his shoulder, "we don't need that pool. We've done it every night since then and we're going to do it tonight as well."

"Mabel, it's not just the sex. It's everything else as well. The way that pool makes me feel about you is… well it's amazing."

"So, what?" Mabel asked as she put her hands on her hips. "You're only sleeping with me because of the way that pool _makes_ you feel?"

"What? No. No!" Dipper realised what he had just said. Destroying Mabel's feelings after they had become so close was the last thing he wanted to do. "I just meant…."

"Relax bro," Mabel laughed. "I'm just teasing. I know what you meant. I feel the same way." Dipper smiled and took Mabel's hands into his own.

"I love you Mabel, and I don't need a magical pond to tell me that. But it's just nice to have somewhere where we can go and be alone for a while, just you and me."

Mabel smiled at her brother, and opened her mouth to say something. But she was cut off with the sound of the door opening, and Grenda and Candy marching into the Gift Shop.

"Hey Mabel," Grenda said, "we packed lunch and was wondering if…" Dipper and Mabel quickly pulled their hands away from each other, but the two girls had already seen it.

"You two seem close today," Candy said as she dropped her back by the desk.

"Yeah, and it's not the first time we've noticed it," Grenda said.

"What… What do you mean? She's my sister." Dipper nervously chuckled.

"You two have been acting slightly odd over the past couple days," Candy said. "We've been noticing it. And you as well," she pointed at Wendy. But unlike Dipper, Wendy kept her cool. Without saying anything, she just picked up a magazine and started to flip through its pages. She had nothing against Mabel's friends, but Wendy didn't like how Mabel could have her friends visit during business hours while she couldn't.

"I, uh… I don't know what you're talking about," Dipper said, his eyes darting from side to side as he desperately looked around for something, anything that he could use to change the topic. He loved his sister, but he still wanted to keep it a secret.

"Okay, now there's definitely something going on," Grenda pointed at Dipper's darting pupils. Mabel placed her hand on Dipper's shoulder as she walked passed him.

"Dipper, come on. They're my friends. I can trust them with this."

"Mabel, don't do it. Please."

"Don't do what?" Candy asked.

"You guys say you brought lunch?" Mabel asked.

"Hey, don't change the subject. What can you trust us with? You can't just say that and not explain it," Grenda said. While she did respect Mabel's privacy and wouldn't argue it, she still wanted to know. Her curiosity had been piped, and now she felt like she _had_ to know.

"Grenda, relax. I'll tell you all about it over lunch. So how about we go into the woods and have a picnic?" Mabel asked, and Candy's face lit up with excitement. It only took a second for Dipper to catch on with what she meant.

"Mabel, don't. We were just talking about this. I thought you didn't want to… Back me up on this Wendy." Dipper panicked. The pond was their spot. He didn't want to have to share it with anyone else. Behind the counter, Wendy just shrugged.

"Hey I told you about it, didn't I? No reason why they can't know."

"No… reason…?" Dipper stammered. He couldn't believe what he was hearing.

"Can't know what?" Grenda asked.

"Tell us." Candy said.

"Guys, don't worry." Mabel said as held her arms out to calm her friends down. "I'll tell you everything over lunch."

"Okay, so where do you want to go?" Grenda asked. Mabel just smiled.

"I was thinking we could go swimming."


End file.
